1. Field of the Invention
The present invention relates to a strain detector that includes a strain-detecting thin-film resistive part provided on a thin plate-shaped strain-generating part formed inside a tubular rigid body via an insulating film and an electrode thin-film provided on the strain-detecting thin-film portion, and a pressure sensor equipped with the strain detector.
2. Description of the Related Art
Pressure sensors have been traditionally used in order to detect fluid pressure or the like. Among the pressure sensors, such a pressure sensor is known that converts pressure of fluid or the like into strain through a thin plate-shaped diaphragm (a strain-generating part), and then takes out signals of the strain as a change of electrical resistance with a strain gauge that is a thin-film resistor formed on the diaphragm.
Various types of thin-film patterns are formed on the diaphragm of the pressure sensor.
For example, an insulating thin film, a thin-film resistor and an electrode thin-film are formed sequentially on a diaphragm that is formed inside a tubular portion, which is an example of prior art (refer to literature 1; Japanese Patent Laid-Open Publication No. 1-235824, FIG. 1, FIG. 2 and others). According to the literature 1, a thin film requiring patterning thereon is provided with a desired pattern by means of photolithography technology and the like, and two strain gauges of thin-film resisters are disposed in the vicinity of center of the diaphragm for receiving tensile strain as well as two are disposed in the vicinity of an edge of the diaphragm for receiving compressive strain, then a thin-film resistance is connected in a full-bridge circuit via electrodes so that electrical signals are taken out.
Further, there is another example of prior art (refer to literature 2; Japanese Patent Laid-Open Publication No. 8-136378, FIG. 1 and others), that is, a strain gauge is disposed in the center of a diaphragm, and electrode pads connected to respective terminals of the strain gauge are arranged along the outer peripheral edge of the diaphragm with offset to one side.
According to the literature 1, the thin-film resistor is connected to the electrode thin-film at electrode connections, and the electrode pad is arranged on the insulating film via the electrode connections where the thin-film resistor and the electrode thin-film are lapped over each other. Since the position of the electrode pad that is the interface between the electrode connection and the electrode thin-film forms a step, hence the electrode thin-film covering the thin-film resistor needs to be thicker than the thin-film resistor, which leads to be expensive. In addition, a step portion of the electrode thin-film is likely to have stress concentration, which causes a drawback of deteriorated electrical connection when forming an external-connection terminal with full-bridge circuit connection of strain gauge.
According to the literature 2, characteristics of a strain detector are examined by contacting an electrode pad portion with a testing probe, and then gold or aluminum wire bonding executes connection to the outside. In this case, a testing probe often damages the electrode pad, which not only causes a poor visual effect but also decreases reliability of wire bonding performed at an identical position of the electrode pad in the post-process.